1. Field of the Invention
This invention relates to a control apparatus for an oil-pressure operated type transmission for a vehicle and, more particularly, to a transmission connected through a torque converter to an internal combustion engine. The transmission has at least two transmission trains of high speed and low speed, each having oil-pressure operated type engaging elements, such as oil-pressure operated type clutches or the like interposed therein and the low speed transmission train is provided with a one-way clutch interposed therein. The control apparatus further includes a creep-preventing means.
2. Description of the Prior Art
In general, in a two-stage transmission having oil-pressure operated clutches, a one-way clutch effectively absorbs a change speed shock at the time of upshifting from the low speed stage. However, at the time of stopping of a vehicle, if idling operation is effected without returning the shift lever to the neutral position, the low speed transmission train is established regardless of the existence or nonexistence of the one-way clutch and the engine torque is transmitted therethrough to driving wheels of the vehicle to cause a creep phenomenon in which the vehicle moves.
For preventing this creep phenomenon, there has been hitherto proposed an arrangement in which a creep-preventing means is operated when an idling operation of the engine, under a vehicle stop condition, is detected so that oil is supplied to cut off the low speed engaging element in the low speed transmission train and automatically return the transmission to its neutral stage. Upon a vehicle starting operation with the accelerator pedal being pushed down, the oil supply to that element is resumed to automatically shift from the neutral stage to the low speed stage. (Japanese Unexamined U.M. Application No. SHO 54-139171). This prior art arrangement, however, is inconvenient in that rapid revving of the engine is caused by a time lag between the time of pushing-down of the accelerator pedal and the time of establishment of the low speed transmission train, and a rapid starting of the vehicle by the establishment of the transmission train with a high speed results in unsmooth vehicle starting.